feat: support external collection schema evolution

[weiliu1031]

issue: #45881

design doc: docs/design-docs/design_docs/20260605-external-table-schema-evolution.md

What changed

This PR supports schema evolution for external collections.

It allows AlterCollectionSchema to update external collection schemas, validates source-backed fields and function-output fields, adds SDK helpers, and records refresh schema versions so stale refresh results are rejected.

It also ensures schema-visible external fields are not served until their backing manifests are materialized. Query/search/index paths now reject unmaterialized fields, QueryCoord schedules loaded segment reopen when manifests are stale, and QueryNode refreshes BM25/function state after schema changes.

Validation

• git diff --cached --check

[sre-ci-robot]

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[sre-ci-robot]

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[sre-ci-robot]

❌ CI Loop Results 80f3ef5

Stage	Result	Duration	Tests
✅ Build	SUCCESS	14.2min	-
❌ Code-Check	FAILURE	2.0min	-
✅ UT-CPP-Cov	SUCCESS	52.5min	7838 passed

Total: 70min | Pipeline | Artifacts
Diff Coverage: CPP 95.5% (42 hit, 2 miss, 44 measurable lines, 30 unmeasured)
Total Patch Coverage: 95.5% (42/44 measurable lines, 30 unmeasured)

[sre-ci-robot]

❌ CI Loop Results 80f3ef5

Stage	Result	Duration	Tests
✅ Build	SUCCESS	14.0min	-
❌ Code-Check	FAILURE	2.0min	-
✅ UT-CPP-Cov	SUCCESS	53.2min	7838 passed

Total: 72min | Pipeline | Artifacts
Diff Coverage: CPP 95.5% (42 hit, 2 miss, 44 measurable lines, 30 unmeasured)
Total Patch Coverage: 95.5% (42/44 measurable lines, 30 unmeasured)

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.21%. Comparing base (1853a14) to head (4452a94).
⚠️ Report is 3 commits behind head on master.

⚠️ Current head 4452a94 differs from pull request most recent head 6622ace

Please upload reports for the commit 6622ace to get more accurate results.

Files with missing lines	Patch %	Lines
...rnal/core/src/segcore/ChunkedSegmentSealedTest.cpp	95.23%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #50394       +/-   ##
===========================================
+ Coverage   78.95%   85.21%    +6.26%     
===========================================
  Files        2239      671     -1568     
  Lines      397069   118431   -278638     
===========================================
- Hits       313503   100923   -212580     
+ Misses      73963    17456    -56507     
+ Partials     9603       52     -9551     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	85.94% <96.87%> (+<0.01%)	⬆️
Go	∅ <ø> (∅)

Files with missing lines	Coverage Δ
internal/core/src/segcore/SegmentLoadInfoTest.cpp	99.00% <100.00%> (+<0.01%)	⬆️
...rnal/core/src/segcore/ChunkedSegmentSealedTest.cpp	99.72% <95.23%> (-0.14%)	⬇️

... and 1570 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[sre-ci-robot]

❌ CI Loop Results cc3325b

Stage	Result	Duration	Tests
✅ Build	SUCCESS	14.1min	-
❌ Code-Check	FAILURE	4.8min	-
✅ UT-CPP-Cov	SUCCESS	52.8min	7838 passed

Total: 69min | Pipeline | Artifacts
Diff Coverage: CPP 95.5% (42 hit, 2 miss, 44 measurable lines, 30 unmeasured)
Total Patch Coverage: 95.5% (42/44 measurable lines, 30 unmeasured)

[sre-ci-robot]

❌ CI Loop Results a2b4384

Stage	Result	Duration	Tests
✅ Build	SUCCESS	9.3min	-
❌ Code-Check	FAILURE	3.8min	-
✅ UT-CPP-Cov	SUCCESS	36.4min	7838 passed

Total: 48min | Pipeline | Artifacts
Diff Coverage: CPP 95.5% (42 hit, 2 miss, 44 measurable lines, 30 unmeasured)
Total Patch Coverage: 95.5% (42/44 measurable lines, 30 unmeasured)

[sre-ci-robot]

❌ CI Loop Results 4452a94

Stage	Result	Duration	Tests
✅ Build	SUCCESS	9.5min	-
✅ Code-Check	SUCCESS	5.9min	-
❌ UT-GO	FAILURE	26.8min	1027 run, failed (details unavailable)
✅ UT-Integration	SUCCESS	24.3min	46 passed
✅ UT-CPP-Cov	SUCCESS	36.8min	7839 passed

Total: 113min | Pipeline | Artifacts
Diff Coverage: CPP 95.5% (42 hit, 2 miss, 44 measurable lines, 30 unmeasured)
Total Patch Coverage: 95.5% (42/44 measurable lines, 30 unmeasured)

Failed Test Logs:

• UT-GO: view log